What Is the Best Way To: Soften Butter?

We are so bad at remembering to set out butter to soften. Then we are standing there, ready to start making a cake or cookies, and oh — the butter's still rock hard. Oops. We often microwave the butter, but sometimes this backfires and melts the butter into a puddle of liquid. How do you soften butter for baking or cooking? Do you have any extra-special tricks for get this done faster?